Experiments will be carried out in pursuit of the original objectives of this research: to screen drugs for activity against Mycobacterium leprae in mice; to carry out pharmacologic studies in mice and other species of drugs previously shown to be active; and to carry out studies of M. liprae itself and of host-parasite relationships in the M. leprae-infected mouse. Among the studies to be carried out are the following: a study of the mechanism of the anti-biotin activity of chaulmoogric acid in broken-cell preparations of M. intracellulare; studies of kinetics of the action of dapsone in mice; a comparison of poly I.C and poly A.U. administered directly into the infected foot pad; studies of the effects of treatment in vitro with heat and rifampin of log-phase and stationary-phase M. leprae and of organisms recovered from dapsone-treated mice; and further studies of the responsiveness to various antigens of lymphocytes from the spleen, popliteal node and peripheral blood of M. leprae-infected mice. BIBLIOGRAPHIC REFERENCES: J. H. Peters, G. R. Gordon, J. T. Biggs and L. Levy. The disposition of dapsone and monoacetyl dapsone in the dog. Proc. Soc. Exp. Biol. Med. 148: 251-255 (1975). L. Levy and N. M. Ullmann. Inhibition of multiplication of Mycobacterium leprae by several antithyroid drugs. Am. Rev. Resp. Dis. 111: 652-655 (1975). L. Levy. Superinfection in mice previously infected with Mycobacterium laprae. Infect. Immun. 11: 1094-1099(1975).